Wire serving is the process of wrapping a wire with an insulating material, e.g., fiberglass, to provide a continuous covering or coating for the wire.
In serving a thread or yarn on to a wire, usually the spool that carries the yarn is mounted on a hollow, rotating spindle through which the wire is drawn in the axial direction, the spindle and spool being rotated at a high speed while the wire passes axially through the spindle so that the yarn is drawn from the spool to be wrapped evenly onto the wire. When the yarn has been drawn completely from a spool, the empty spool is destroyed and is replaced by a new spool so that the winding may be continued without cutting the wire.
Often a wire serving process will have a ribbon composed of several threads dispensed from a single spool which is wrapped around a wire. When such thread ribbons are used, the function of the thread spool becomes more important in maintaining the consistency and operativeness of the thread ribbon. Any slackening of the various threads or even nonuniformity in the tension of the various threads will allow the ribbon to separate into individual strands and thereby cause gaps in the ribbon.
In order to make sure that the tension is maintained on all of the strands of the ribbon, the spool dispensing the thread ribbon must be accurately and fixedly positioned with relation to the wire. Further, the winding on the spools must be absolutely uniform.
If the axial or radial dimensions of the spools or the windings of thread on the spool varies, then the thread will be fed off the spool in different lengths as the spool revolves, causing unacceptable irregularities in the thread ribbon. Therefore, the dimensions of the spool and the dimensional stability of the spool and thread windings on the spool are of great importance to insure that the thread windings are equal and uniform. For example, if the flanges of the spool are not rigidly constructed the windings of thread can become uneven at the juncture of the hub section of the spool with the flange sections. This can result in a barrel-shaped thread winding on the hub of the spool with the radius of the thread winding being greater at the center than at the ends of the hub. The dimensional imprecision or instability of the flanges could also result in the thread windings on the hub being of uneven length between one layer of the winding and the next.
Another problem that exists with the presently available spools is when they become empty they must be broken to remove them from the spindle. Inevitably, the spools break up into pieces which may have jagged edges that can injure an operator. Additionally the action of breaking the spool results in pieces of the spool flying in the work area and causing a safety hazard.
Efforts have been made in the past to control the breakage of the spools by placing slots or grooves in the spool. However, while not solving the hazards of breakage, in addition, these slots and grooves can weaken the spool and make it prone to premature breakage.
Several spools have been designed to try and overcome these problems.
In U.S. Pat. No. 3,270,980 to Philips, a spool is described having a hub, adapted to fit on a spindle, and flanges at each end provided with grooves which facilitate fracturing and ready removal of the spool when empty.
Another such spool is described in U.S. Pat. No. 3,635,421, to Boland et al. This spool has two halves, each of which includes a flange and a hub half which has a semi-circular cross-section connected to and extending from the flange with complementary tongues and grooves formed along the longitudinal mating surfaces thereof. An inner face of each flange is provided with an arcuate recess for receiving a free end of the mating hub half.
The spool is assembled by aligning the mating tongues and grooves and then moving the halves slideably into engagement with each other to connect together the halves and then securing the halves together by inserting the free end of each hub half into the recess in the flange of the mating half. Disassembly follows the same procedure in reverse. The outer face of each flange is formed with inclined portions or surfaces, so that as the spool is rotated with the spindle, the flange is subjected to air pressures which maintain the spool on the spindle in a generally fixed position along the longitudinal axis of rotation.
A problem of the Boland spool is the lack of adaquate means to fix the dimensional stability of the distance between the flanges.
U.S. Pat. No. 3,105,655 to Park et al describes a solid spool having a slit in the core extending for the full length of the core and having end flanges which are frangible so that they may be readily broken to permit removal of the empty spool.
Other patents which deal with the spools that can be broken down but which do not meet the problems addressed by the present invention are U.S. Pat. No. 2,648,507 to Kitrow; U.S. Pat. No. 2,693,323 to Jarmicki; U.S. Pat. No. 2,777,648 to Wood; U.S. Pat. No. 2,858,999 to Guenther, Jr.; U.S. Pat. No. 3,105,655 to Park et al; U.S. Pat. No. 3,358,943 to Pelson; U.S. Pat. No. 3,635,421 to Boland et al; U.S. Pat No. 3,940,085 to Campbell; U.S. Pat. No. 3,966,139 to Terpak; U.S. Pat. No. 4,068,808 to King.